High-pressure synthesis and neutron diffraction investigation of the crystallographic and magnetic structure of TeNiO3 perovskite

Abstract

TeNiO₃ has been prepared under moderate pressure conditions (3.5 GPa), starting from a reactive TeO₂ and Ni(OH)₂ mixture contained in a sealed platinum capsule under the reaction conditions (850 °C for 2 h). The sample has been studied by neutron powder diffraction (NPD) data and magnetization measurements. TeNiO₃ crystallizes in an orthorhombically-distorted perovskite structure (space group Pnma) with the unit cell parameters a = 5.9588(1) Å, b = 7.5028(1) Å and c = 5.2143(1) Å. The NiO₆ octahedral network is extremely tilted, shaping a trigonal-pyramidal environment for the Te, where it is effectively coordinated to three oxygen atoms at Te–O distances of 1.92 Å. Below T_N ≈ 130 K, it experiences an antiferromagnetic ordering, as demonstrated by susceptibility and NPD measurements. Above the Néel temperature, a paramagnetic moment of 3.24(1) μ_B/f.u. and θ_Weiss = −199(1) K are obtained from the reciprocal susceptibility. Below T_N, the magnetic reflections observed in the neutron patterns can be indexed with a propagation vector k = 0. The magnetic structure corresponds to the magnetic mode G_yF_z. The magnetic moments are oriented along the y-direction, with a canting along the z-axis. This ferromagnetic component explains the weak ferromagnetism observed in the magnetization isotherms; the infrequent shape of the magnetization cycles suggests a metamagnetic transition below 0.2 T. At T = 2.5 K, the ordered magnetic moment for the Ni²⁺ ions is 1.88(5) μ_B for the G_y mode and 0.9(2) μ_B for the F_x mode.